System for testing the upstream channel of a cable network

ABSTRACT

A system for testing a portion of a cable network provides a pattern generator, addresser, forward error corrector, and comparator. The system is particularly adapted to testing the upstream channel in a cable network. The pattern generator generates a test signal. The addresser addresses the signal to a known server and also instructs the known server to return the test signal to the test system. The forward error corrector corrects errors introduced in the test signal in transmission from the known server to the test system. The comparator then compares the returned test signal to the originally transmitted test signal to determine the performance of the back channel. Preferably, the comparator uses a bit error rate test to determine the performance of the back channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non Provisional patentapplication Ser. No. 12/371,505 filed Feb. 13, 2009, which is acontinuation of U.S. Non Provisional application Ser. No. 11/164,247filed Nov. 15, 2005, now U.S. Pat. No. 7,509,542 B2, which is acontinuation of U.S. Non Provisional application Ser. No. 09/704,888,filed Nov. 1, 2000, now U.S. Pat. No. 7,010,730 B1 and the subjectmatter thereof is hereby incorporated herein by reference thereto.

FIELD OF THE INVENTION

The present invention relates generally to a system for testing theupstream channel transmission facility in a cable network. Morespecifically, the present invention provides for bit error rate testingof the upstream channel of a cable network.

BACKGROUND OF THE INVENTION

Originally cable networks were established to transmit televisionsignals to homes and offices. Cable networks provide advantages overtransmission television networks that include a clearer signal and agreater selection of channels. These cable networks originally wereintended simply to provide customers with television signals. Therefore,they did not provide customers a means to transmit signals to the cablenetwork operator, to other customers, or to any other party.

In early embodiments, cable networks transmitted analog signals. Morerecently, cable networks have been converted to transmit digitalsignals. With digital cable networks, customers may transmit signalsback to the cable network operator. This facility has been called theupstream channel in contrast to the forward or downstream channel thatdelivers programming to the customer. Additionally, digital cablenetworks may now be coupled to the Internet thereby providing houses andoffices access to the Internet. This access is generally faster thanaccess provided by other technologies.

FIG. 1 shows a typical digital cable network. A cable modem terminationsystem (“CMTS”) 100 is the base component of the system. The CMTS 100 isa typical system well known in the art and typically includes facilitiesfor forward error correction. The CMTS 100 is coupled to the Internetbackbone 102. The Internet backbone 102 carries Internet traffic, iswell known in the art, and typically comprises fiber optic communicationlines. Alternatively, the Internet backbone 102 may comprise co-axialcables. CMTS 100 is also coupled to a combiner/splitter 116.Combiner/splitter 116 combines signals from CMTS 100 and from fiberoptic lines 104. Fiber optic lines 104 carry television signals. Fiberoptic lines 104 may alternatively be co-axial cables. Combiner/splitter116 is well known in the art. Combiner/splitter 116 combines signalsfrom the Internet backbone 102 and the incoming television signals fromfiber optic lines 104 and outputs a resulting signal on a fiber optictransmission line 106. Combiner/splitter 116 also receives signals fromfiber optic transmission line 106 and splits off the appropriate signalsfor transmission to the Internet backbone 102 or for use by the cablenetwork operator. Fiber optic transmission line 106 is a standard cablenetwork transmission line comprising fiber optics and related equipment.

Fiber optic transmission line 106 is coupled to one or more nodes 108.In an alternative embodiment, a co-axial cable couples combiner/splitter116 to nodes 108. Nodes 108 serve as distribution points for the cablenetwork receiving signals from the CMTS 100 transmitted on the fiberoptic transmission line 106. Each node 108 is coupled to a local areacable loop (“LACL”) 110. LACL 110 is typically a co-axial cable thatcarries signals from the node to homes and businesses within in arelatively close geographical area. Alternatively, LACL 110 may be afiber optic cable. LACL 110 forms a loop with its beginning and endcoupled to node 108. Node 108 retransmits signals received fromcombiner/splitter 116 on its associated LACL 110. In alternateembodiments, LACL 110 may be coupled directly to combiner/splitter 116.Those of ordinary skill in the art will recognize that a network mayhave many different structures.

Coupled to each LACL 110 are one or more customer sites 112. A customersite may be either a home or office and is coupled to LACL 110 by aco-axial cable 114 that taps off of LACL 110.

FIG. 2 shows the coupling of LACL 110 to a plurality of customer sites112 and to node 108. Node 108 has two couplings to LACL 110, 200 and 202respectively. Couplings 200 and 202 are logical couplings; in actuality,a single fiber optic transmission line or co-axial cable couples node108 to LACL 110. FIG. 2 also shows a customer site in more detail.Corresponding to couplings 200 and 202 are couplings 204 and 206.Couplings 204 and 206 are logical representations of the couplingbetween customer site 112 and LACL 110. In actuality, the couplingbetween customer site 112 and LACL 110 is a coaxial cable, twisted pair,wireless, or other coupling. Coupling 204 provides a forward ordownstream channel signal path from LACL 110 to customer site 112.Correspondingly, coupling 206 provides an upstream signal path fromcustomer site 112 to LACL 110 and then to node 108 and CMTS 100.

Customer site 112 comprises a combiner/splitter 214, a cable modem 208and at least one computer 210 and at least one television 212. Computer210 is well known in the art and is equipped with a browser fortransmitting to and receiving information from the Internet. Computer210 is coupled to cable modem 208. Cable modem 208 is a conventionalcable modem. Cable modem 208 is coupled to combiner/splitter 214 whichis a conventional device for combining and splitting digital signals.Combiner/splitter 214 is similar to combiner/splitter 116 but on a scaleappropriate for a customer site. Those of ordinary skill in the art willrecognize combiner/splitter 214. Television 212 is also coupled tocombiner/splitter 214.

Coupling 200 provides a forward channel signal path from node 108,through LACL 110, through coupling 204, and to the customer site 112. Inthe forward channel, the node transmits digital signals at frequenciesbetween 88 and 860 MHz. Typically, the forward channel provides forwarderror correction whereby cable modem 208 is capable of detecting errorsin the signal it receives from node 108. Having detected errors in thesignal, cable modem 208 then corrects the errors. The methods and meansfor correcting signals received by a cable modem are well known in theart.

Coupling 202 provides a signal path for customer sites 112 tocommunicate with the cable network operator. Cable modem 208 transmitsthrough coupling 206, through LACL 110, and through coupling 202 in thereverse direction of the forward channel through coupling 202. Thisupstream channel is generally limited to frequencies between 5 and 50MHz. Historically, the cable network operators used the upstream channelto provide a signal path from customer sites 112 to the cable networkoperator. For example, a customer site may request specific programming,sometimes known as pay per view. A customer site may also use theupstream channel to send other requests to the cable network operatorsuch as billing inquiries, notices of service deficiencies, and otherinformation.

FIG. 3A illustrates the form of a signal 300 in the forward channel fromcombiner/splitter 116 to a customer site. The forward channel signal isthe result of time multiplexing more than one serial signal. FIG. 3Ashows three exemplary signals 302 that are time multiplexed into a downstream signal 300. The forward channel signal is framed with each framelead by a header 304. The header 304 indicates the beginning of theframe and the remaining bits of the frame are the payload. The signal toeach customer site is time multiplexed with the signals intended forevery other customer site on the LACL and loaded into the payload of theframe. The cable modem at each customer site monitors the forwardchannel signal and picks off the bits in the payload of each frame thatare intended for the specific cable modem. The cable modem thenreconstructs the signal intended for the customer site. There are manymethods of time multiplexing signals; those of ordinary skill in the artwill recognize these methods.

The upstream channel is typically not framed. FIG. 3B illustrates theform of an upstream channel signal 306 that comprises packetstransmitted in a token ring type protocol. When a cable modem firstcouples to a LACL, it receives a schedule from the CMTS. This scheduledesignates when the cable modem may transmit in the upstream channel.When the schedule indicates that the cable modem may transmit in theupstream channel, the cable modem composes a packet and transmits it inthe reverse direction of the forward stream to the CMTS.

A packet comprises a packed identifier (“PID”) 308 and a payload 310.The PID 308 specifies the cable modem that transmitted the packet,specifies the destination of the packet, and may include otherinformation. The payload 310 of the packet comprises entirely data fromthe transmitting cable modem. Unlike the forward channel signal,upstream channel packets are typically not multiplexed with signals fromother cable modems; the entire packet payload comprises data from asingle cable modem.

As mentioned above, the upstream channel was originally intended to beused for sending requests to the cable network operator and hasgenerally not provided high transmission performance. A customer site,however, would typically transmit infrequently and then would transmitonly small amounts of data. The upstream channel, therefore, wasgenerally not crowded and performance was not a priority.

More recently, cable network operators have coupled CMTSs to theInternet backbone to provide customer sites with Internet access.Generally, such systems have offered advantages over other technologiesfor coupling customer sites to the Internet. The forward channel has alarge bandwidth that allows for fast downloads of data to customersites. Additionally, cable systems are already in place; removing thenecessity of large capital investment. At first, the limited performanceof the upstream channel was not an impediment to using cable systems forInternet access. Generally, Internet traffic from a customer site to theInternet backbone required much less bandwidth than the forward streamrequired. Customer sites would make requests to web sites for data. Therequests, being small, would not require broad bandwidth. The requesteddata, however, would frequently be large and require the broad bandwidthof the forward channel. The poor performance of the upstream channel wasnot relevant to the use of cable systems for Internet access. If asignal from a customer site never reached its destination, the customersite simply sent the signal again. The size of signals and their numberdid not noticeably impede Internet access.

More recently, however, the limited performance of the upstream channelis impeding Internet access. Customer sites are transmitting more datain the upstream channel. Some customer sites now are themselves websites or are uploading large amounts of information to the Internet.Thus, the amount of data transmitted in the upstream channel hasincreased. Additionally, there are more customer sites accessing theInternet; correspondingly there is more traffic in the upstream channel.The greater number of customer sites means fewer transmission slots forany one customer site; should a signal need to be retransmitted, therewill be a delay until another transmission slot is available. Also, theincreased size of the signals makes them more burdensome to resend. Nolonger is it acceptable simply to resend a signal that fails to reachits destination. In order to utilize fully the capabilities of a cablenetwork, impairments that result in retransmission of packets in theupstream channel must be diagnosed and repaired.

It has become imperative to improve the performance of the upstreamchannel in cable networks. With the need to improve upstream channelperformance, there is a corresponding need to test the upstream channel.Testers are needed to determine when and where the upstream channel islimiting network performance. The upstream channel is difficult to test.At this time, when a customer site is experiencing inadequate Internetaccess, a test set must be used at the customer site and simultaneously,a test set must be used at the CMTS, the node, or other location. Theneed to coordinate multiple test sets makes testing the upstream channeldifficult. In addition, disabling the network while testing is notpractical. There is a need for devices and methods to test accuratelyand efficiently the upstream channel of cable networks without disablingthe network while testing.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a system fortesting the upstream channel of a cable network. It is a furtherobjective of the present invention that the system provide automaticdetermination of the performance of the upstream channel withoutdisabling the network for other users during testing. Finally, it is anobjective of the present invention to provide a system for testing theupstream channel without the need for a second coordinated test deviceat the CMTS location.

The present invention utilizes the forward error correction facility ofcable networks to provide a novel system for testing the upstreamchannel of a cable network. In its most basic form, the presentinvention provides a tester that comprises a pattern generator,addresser, forward error corrector, and comparator. The patterngenerator generates a signal that the tester transmits on the upstreamchannel. A device within the Internet backbone, selected by theaddresser, receives the signal from the pattern generator and returns itto the tester. At the tester, the forward error corrector removes errorsintroduced in the forward channel. The comparator then compares thecorrected, received signal to the signal originally transmitted. Thecomparator determines, through tests such as a bit error rate test, theperformance of the upstream channel.

The present invention provides a device for testing the upstream channelthat is efficient, that may be used without disabling the network, andthat does not require a second, coordinated test device at the CMTSlocation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional cable network.

FIG. 2 is a block diagram of a local area cable loop with a detailedillustration of a customer site.

FIG. 3A is a block diagram of the form of the forward channel signal ina conventional cable network.

FIG. 3B is a block diagram of the form of the upstream channel signal ina conventional cable network.

FIG. 4 is a block diagram of a local area cable loop with the presentinvention included.

FIG. 5 is a block diagram of a tester according to the presentinvention.

FIG. 6 is a block diagram of the memory of a tester according to thepresent invention.

FIGS. 7A & 7B are flow charts of the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 4, a Tester 400 according to the present inventionis shown coupled to LACL 110. Preferably the Tester 400 is handheld orportable making it convenient for a user to transport to a customersite. Tester 400 is coupled through logical coupling 204 so that it mayreceive signals from the forward channel on LACL 110. Tester 400 is alsocoupled through logical coupling 206 to transmit signal on the upstreamchannel of LACL 110. In the preferred embodiment, Tester 400 is coupledto LACL 110 by a coaxial cable or twisted pair. It is preferred thatTester 400 be coupled to LACL 110 in place of the cable modem 208 at thecustomer site 112. This, however, is not required. Tester 400 may becoupled to LACL 110 at any location. Tester 400 advantageously tests theupstream channel without disrupting other traffic in the upstreamchannel.

Referring now to FIG. 5, a detailed view of an embodiment of Tester 400is shown. Tester 400 comprises a cable modem 500, a processor 502, amemory 504, a transmit port 506, a receive port 508, a bus 510, and anoutput device 512. While FIG. 5 shows an embodiment of Tester 400, thoseof ordinary skill in the art will recognize that Tester 400 may beembodied in field programmable gate arrays, application specificintegrated circuits, and many other components.

Processor 502 is a conventional microprocessor for executinginstructions in computer or an electronic device. Microprocessors areavailable from Intel Corporation of Santa Clara, Calif., from Motorola,Inc. of Schaumburg, Ill., or from many other manufacturers. In somecases, microprocessors are integrated, along with other circuits, intocustom, commercially available application specific integrated circuits.Memory 504 is preferably a conventional static random access memorydevice but alternatively may be any memory device including, but notlimited to, a cd-rom, a read only memory, a dynamic random accessmemory, a hard drive, a floppy drive, a magnetic tape, a programmableread only memory, an electronically programmable read only memory, anerasable electronically programmable read only memory, or a flashmemory. Those of ordinary skill in the art will recognize that memory504 may be any type of data storage device.

Memory 504 is uniquely programmed with instructions that, when executedby the processor 502, implement the present invention. A conventionalbus 510 couples processor 502 to memory 504. Output device 512 is aconventional output device such as a computer monitor and is coupled toprocessor 502 and memory 504 by bus 510.

The bus 510 also couples the processor 502, output device 512, andmemory 504 to cable modem 500. Cable modem 500 is a conventional cablemodem for transmitting and receiving signals on a cable network. Cablemodems are available from Broadcom Corporation of Irvine, Calif. Cablemodem 500 both receives and transmits signals to and from the processor502 and memory 504. Cable modem 500 is also coupled to a port 506 totransmit signals through logical coupling 206 to LACL 110. Similarly,cable modem 500 is coupled to a port 508 to receive signals, throughlogical coupling 204, from LACL 110.

According to the present invention, cable modem 500 may include systemsfor forward error correction of the forward channel signal receivedthrough port 508. Forward error correction techniques are well known inthe art.

Referring now to FIG. 6, a block diagram of memory 504 is shown. Memory504 comprises a pattern generator 600, an addresser 602, a comparator604, and a forward error corrector 606. Those of ordinary skill in theart will realize that pattern generator 600, addresser 602, comparator604, and forward error corrector 606 are sections of memory 504 thathold program instruction steps that when executed by the processor 502carry out the functions of the devices. Pattern generator 600, addresser602, comparator 604, and forward error corrector 606 are coupled to theprocessor 502 and cable modem 500 through bus 510. In this embodiment,forward error corrector 606 is located in memory 504; in an alternate,and preferred, embodiment, forward error corrector is located in cablemodem 500.

Pattern generator 600 generates a test signal for transmission in theupstream channel of LACL 110. Preferably, pattern generator 600generates a pseudo random test signal, but any signal will suffice.Pattern generator 600 then transmits the test signal to addresser 602and to comparator 604. The copy of the test signal that patterngenerator 600 transmits to comparator 604 serves as a standard for thetests Tester 400 conducts. Addresser 602 prepares the test signal fortransmission on LACL 110. Addresser 602 loads the test signal into thepayload of one or more packets for transmission in the upstream channel.Addresser 602 also prepares the PID of each packet. Included in the PIDis that address of the location to which the packet is beingtransmitted, the destination of the packet. Preferably addresser 602addresses the packets to CMTS 100 although addresser 602 may address thepackets to other destinations. Addresser 602 also includes within thePID an instruction for the device at the destination to return the testsignal to cable modem 500. Addresser 602 then provides the test signalto cable modem 500 for transmission on LACL 110.

When the CMTS 100 returns the test signal to Tester 400, Tester 400receives the returned signal through the forward channel and throughcable modem 500, which then passes the test signal to forward errorcorrector 606. Forward error corrector 606 uses conventional techniquesto remove errors from the test signal introduced in the test signalduring transmission in the forward channel from CMTS 100. Forward errorcorrector 606 then passes the corrected test signal to comparator 604.

Comparator 604 first eliminates the PIDs so that only the test signal inthe payload remains. Comparator 604 then compares the corrected testsignal to the original test signal received from pattern generator 600.One of the techniques comparator 604 uses is the bit error rate test.The bit error rate test is the quotient of the number of errors in asignal divided by the number of bits in the original signal. Here, thebit error rate test is determined by dividing the number of errors inthe corrected signal by the number of bits in the original test signal.Comparator 604 determines the number of errors by comparing the originalsignal from pattern generator 600, which serves as a standard, to thecorrected signal from forward error corrector 606. Deviations betweenthe original signal from pattern generator 600 and the corrected signalfrom forward error corrector 606 are errors.

Having determined the bit error rate, comparator 604 transmits a signalto output device 512, shown in FIG. 5. Output device 512 then outputsthe result of the test. Those of ordinary skill in the art willrecognize that comparator 604 may execute many other tests on thecorrected test signal in addition to the bit error rate test.

In an alternate embodiment, comparator 604 uses a block error rate test.The block error rate test is the quotient of the number of packets thatreach CMTS 100 with errors divided by the number of packets addresser602 transmits. In this alternate, and less preferred embodiment, whenthe addresser 602 addresses a packet, it includes an index in the PID.The index indicates where in the sequence of packets that comprise thetest signal the particular packet exists. For example, for the firstpacket of the test, the addresser 602 would insert the index 1 in thePID. For the second packet, the addresser 602 would insert 2, and so on.In the block error rate test, the CMTS 100 uses forward error correctiontechniques to detect if any errors have been introduced into the packetsthat it receives from the addresser 602. If an error has occurred in apacket, the CMTS 100 discards the packet. If no error has occurred inthe packet, the CMTS 100 transmits it back to the Tester 400. Comparator604 determines the number of packets in which errors occurred in theupstream channel using the indices in the PID of the returned packets.The comparator 604 then determines the block error rate which is thequotient of the number of discarded packets divided by the number ofpackets transmitted. In this alternate embodiment, the forward errorcorrector 606 is not necessary except to correct errors, which occurredin the forward channel, in the index.

The preferred embodiment of the system of the present invention is asincorporated in a cable modem application specific integrated circuit(“ASIC”) from Broadcom Corporation of Irvine, Calif. Broadcom providesASICs with basic cable modem functionality along with means to programthe ASIC with additional functionality. It is preferred that aprogrammable Broadcom cable modem ASIC be programmed to include patterngenerator 600, addresser 602, comparator 604, and forward errorcorrector 606.

FIGS. 7A & 7B illustrate a flow chart of the preferred method fortesting the upstream channel of a LACL. The preferred method begins atstep 700 where the method determines if the user has indicated that thetest is to terminate. The preferred method runs continuously untilstopped by an operator. As explained below, the longer the method runsthe more accurate will be its result. If, in step 700, the method hadreceived a signal to terminate the test, the method ends. Otherwise, instep 702, the method generates a test signal. The test signal ispreferably of sufficient length to fill the payload of the largestpacket that is available for the local area cable loop to be tested. Instep 704, the method prepares the PID of the packet or packetscontaining the test signal. Preparing the PID includes addressing thepacket or packets to a destination server. Preferably the destinationserver is the CMTS although it may be another server. In step 706, thePID is also set to instruct the destination server to return the packet.Each packet that contains the test signal has a similarly prepared PID.

The method in step 708 transmits the packets in the upstream channel ofthe LACL. In step 710, the packets are returned to their source in theforward stream of the local area cable loop. Errors introduced into thesignal as it was transmitted in the forward channel from the CMTS arecorrected in step 712. The methods of forward error correction ofsignals in the forward channel are well known in the art. Those ofordinary skill in the art will recognize that forward error correctiontechniques are only capable of correcting errors to a point. If thenumber of errors exceeds a threshold number, the forward errorcorrection technique cannot correct all the errors. The technique can,however, determine if residual errors, errors that were not corrected,are present. Additionally, the forward error correction techniques canonly correct errors introduced in the forward stream from the CMTS tothe tester. It is preferable to correct all errors introduced into thesignal that were not introduced in the upstream channel. For thesereasons, it is preferable in step 704 to address the test signal to theCMTS. All errors not occurring in the upstream channel will thereby becorrected or otherwise eliminated as described below.

In step 714, the method determines if any residual errors are present inthe corrected signal. If there are residual errors, the method discardsthe portion of the signal that contains the residual errors in step 716and returns to step 700. In an alternate embodiment, the method does notdiscard the portion of the signal containing errors; the alternatemethod simply accepts the inaccuracy. In yet another alternateembodiment, it is possible to correct for the residual errors. If thenumber of residual errors is regular, the method may identify theregularity and adjust the result determined in step 718, describedbelow, accordingly.

If in step 714 no residual errors are present, the preferred method, instep 718, compares the returned test signal to the originally generatedtest signal which serves as a standard. From the comparison it ispossible to measure the performance of the upstream channel because allerrors in the signal occurred in the upstream channel. Any errors thatoccurred in the forward channel were either corrected in step 712 orwere discarded in step 716.

The preferred test for determining the performance of the upstreamchannel is a bit error rate test. The bit error rate test is thequotient of the number of errors in the signal divided by the number ofbits in the signal. The number of errors is determined by comparing thecorrected signal to the standard. Deviations between the correctedsignal and the standard are errors. Preferably the bit error rate testis determined using all errors detected and all bits transmitted fromthe beginning of the test.

An alternate test at step 718 is the block error rate test. For thisalternate, and less preferred test, in step 704 the method includes anindex with the packet. The index indicates how many packets, as of thattime, the method has transmitted in the upstream channel. For example,the first packet has index 1, the second packet has index 2, et cetera.In this alternate method, the destination CMTS discards packets in whicherrors occurred in the upstream channel. The CMTS returns packetswithout errors. Upon receipt of the returned packets, the method neednot correct errors, although if an error occurred in the index, themethod may use forward error correction to correct the index. The methoduses the indices to determine how many packets the CMTS has discarded.For example, if a packet returns with index 100 and the next packet toreturn has index 111, then the method determines that the CMTS discarded10 packets. The block error rate is the quotient of the number ofpackets discarded divided by the number of packets transmitted. For theblock error test, the method preferably transmits packets that are assmall as possible. Those of ordinary skill in the art will realize thatmany other measurements, in addition to the bit error rate test and theblock error rate test, are possible.

In step 720, a signal indicative of the performance of the upstreamchannel is output to update the test result. As FIGS. 7A & 7B show, thepreferred method loops, testing continuously until it receives atermination signal. By looping and using all errors detected and allbits transmitted, the longer the test runs, the more accurate it willbe. In step 708 the method maintains a count of packets transmitted, andin step 718, the method maintains a count of bit errors introduced inthe upstream channel. In the alternate method, step 718 maintains acount of packets that the CMTS has discarded. The method loops byreturning to step 700.

1. A device for determining the performance of a portion of a networkcomprising: a transmitter for receiving transmitter transmitted signalsback from a remote receiver, the transmitter including: a forward errorcorrector for correcting errors introduced into the transmittertransmitted signals from the remote receiver to the transmitter; and acomparator coupled to the forward error corrector for comparing atransmitted signal and the transmitter transmitted signals from theremote receiver for determining the performance of the portion of thenetwork from the remote receiver to the transmitter.
 2. The device ofclaim 1 further comprising a pattern generator connected to the network.3. The device of claim 1 wherein the network is a cable network.
 4. Thedevice of claim 3 wherein the portion of the cable network is a localarea cable loop.
 5. The device of claim 4 wherein the device is coupledto an upstream channel of the local area cable loop.
 6. The device ofclaim 5 wherein the device is also coupled to a forward channel of thelocal area cable loop.
 7. The device of claim 1 further comprising anaddresser connected to the network.
 8. The device of claim 5 furthercomprising an addresser connected to the network.
 9. The device of claim1 further comprising: a pattern generator coupled to the comparator; andan addresser coupled to the pattern generator.
 10. The device of claim 3further comprising a cable modem termination system in the network. 11.The device of claim 9 wherein: the network is a cable network; theportion of the network is a local area cable loop; and the addresser iscoupled to an upstream channel of the local area cable loop.
 12. Adevice for determining the performance of a portion of a networkcomprising: a transmitter for receiving transmitter transmitted signalsback from a remote receiver, the transmitter including: circuitry forcorrecting errors for correcting errors introduced into the transmittertransmitted signal from the remote receiver to the transmitter; andcircuitry for comparing a transmitted signal and the transmittertransmitted signals from the remote receiver for determining theperformance of the portion of the network from the remote receiver tothe transmitter, the circuitry for comparing connected to the circuitryfor correcting errors.
 13. The device of claim 12 further comprisingcircuitry for generating the transmitted signal connected to thenetwork.
 14. The device of claim 12 wherein the network is a cablenetwork.
 15. The device of claim 14 wherein the portion of the cablenetwork is a local area cable loop.
 16. The device of claim 12 furthercomprising circuitry for addressing a signal to the remote receiver, thecircuitry for addressing connected to the network.
 17. The device ofclaim 16 wherein the destination is a cable modem termination system.18. A memory device for storing program instructions comprising: atransmitter for receiving transmitter transmitted signals back from aremote receiver, the transmitter including: a forward error correctorfor correcting errors introduced into the transmitter transmittedsignals from the remote receiver to the transmitter; and a comparatorcoupled to the forward error corrector for comparing a transmittedsignal and the transmitter transmitted signals from the remote receiverfor determining the performance of a portion of a network from theremote receiver to the transmitter.
 19. The memory device of claim 18further comprising program instructions for a pattern generatorconnected to the network.
 20. The memory device of claim 19 furthercomprising program instructions for an addresser connected to thenetwork.
 21. The memory device of claim 18 further comprising programinstructions for an addresser connected to the network.